The demand for wireless communication systems has grown steadily over recent decades, and has included several technological jumps over this time, particularly in the area of cellular and wireless local area network (WLAN) communication systems. Analogue cellular phones have been replaced with digital handsets using for example GSM and CDMA technologies, and so called third generation systems such as UMTS are now being introduced. Similarly WLAN technologies such as HyperLan and IEEE 802.11b are also being introduced. The number of users continues to increase and data traffic is now becoming an important part of the wireless network. Both of these factors mean that it is important for operators to look for methods of increasing the capacity of their networks to meet future demands.
An increasing demand to access the internet and other data networks has led to the need for increased capacity particularly in the downlink direction. That is, increased capacity from basestations to wireless user terminals in order that users are able to download web pages and other information. One way of addressing this problem is to use multiple input multiple output (MIMO) systems which are able to provide increased data rates. These systems involve using a plurality of antennas on both the transmitter and receiver and the problem of how to accommodate such structures in user terminals, which are often required to be hand held then arises.
In our earlier U.S. patent application Ser. No. 09/765,532, filed on 19 Jan. 2001 and also assigned to Nortel Networks, we describe an antenna arrangement for use in a laptop computer to provide MIMO communications. Three or four antennas are provided around the edges of the screen part of the laptop computer which is preferably oriented vertically when in use. The antennas are all integrated into the body of the laptop where the body includes the screen part. Transmission line loaded antennas are used such as bent folded monopoles or planar inverted F antennas. Each antenna has a monopole section which is perpendicular to a ground plane. Whilst the systems described in Ser. No. 09/765,532 are fully workable the present invention seeks to extend our earlier work.
Considering hand-held user terminals such as personal digital assistants (PDAS) these are currently available from a range of manufacturers such as Palm, Handspring and IBM. Some PDAs such as the Palm VIIx are provided with wireless communications capability, either using a transceiver built into the PDA, or by mounting the PDA in a separate cradle. However, these systems provide a single channel wireless solution in the same way as conventional mobile terminals rather than enabling MIMO communications.
The invention seeks to provide an antenna arrangement suitable for user terminal multiple-input multiple-output radio communications systems which overcomes or at least mitigates one or more of the problems mentioned above.
Further benefits and advantages of the invention will become apparent from a consideration of the following detailed description given with reference to the accompanying drawings, which specify and show preferred embodiments of the invention.